Weak localization in the layered iridatesSr2Ir1−xMxO4(M=Ru,Ti): Role of interplay between spin-orbit coupling and magnetism

Abstract

The combined role of the spin-orbit effect (SOC), electron correlation ($U$), and magnetism has had a significant impact on the electron transport behavior in disordered systems. Here, we report an experimental investigation of weak localization (WL) behavior in layered SOC-dominated iridate ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ where these impacting parameters are further tuned with substitution of Ru and Ti, which have different magnetic and electronic characters. Magnetic ${\mathrm{Ru}}^{4+} (4{d}^{4})$ participates in magnetic interaction with existing ${\mathrm{Ir}}^{4+}$ as well as with itself, while nonmagnetic ${\mathrm{Ti}}^{4+} (3{d}^{0})$ will lead to the dilution of a magnetic lattice. ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ shows a crossover from negative to positive magnetoconductivity (MC) with the onset of magnetic ordering where the WL behavior is observed in a magnetically ordered state. In ${\mathrm{Sr}}_{2}{\mathrm{Ir}}_{1\ensuremath{-}x}{\mathrm{Ru}}_{x}{\mathrm{O}}_{4}$ series, a complete suppression of the magnetic and insulating state is observed with $x\ensuremath{\sim}0.6$. However, an opposite result is seen in ${\mathrm{Sr}}_{2}{\mathrm{Ir}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{4}$ series, where the magnetic ordering temperature is minimally influenced, though the magnetic moment is weakened and the insulating state is significantly strengthened. This contrasting effect on magnetism has a different impact on the crossover in MC and allied WL behavior, which basically follows the evolution of the magnetic and conducting state in both series. The ${\mathrm{Ti}}^{4+}$ further reverses the negative MC in the nonmagnetic state to positive MC with a reduction in SOC. This work demonstrates the critical role of magnetism, SOC, and $U$ in manipulating the quantum transport properties in one of the iridate materials which we believe has significance in other similar materials.